The present invention relates to a method and apparatus for spin bonding a synthetic plastic end closure member to one end of a composite container body member, and to the resultant product. The concept of spin bonding, or friction welding as it is alternately termed, of two synthetic plastic parts, for instance a container body and an end closure or cap member, is known, as disclosed in the patent to Brown, U.S. Pat. Nos. 3,297,504 and 3,499,068, Jones, U.S. Pat. No. 3,712,497, and Standley, U.S. Pat. No. 4,075,820. Generally, the two synthetic plastic parts are of substantially equal thickness so that when they are spinning in frictional engagement, the heat created is sufficient to soften and subsequently bond the parts.
Owing to the relatively small thickness of the inner liner layer, the spin bonding of a synthetic plastic end closure member to a composite container body member presents certain inherent problems. More particularly, the end closure member is generally at least 50 times thicker than the thermoplastic inner liner layer, and in the past, prior attempts to spin bond the two parts together have been generally unsuccessful. Thus, the thin thermoplastic inner layer is often either torn or disturbed from its engagement with the composite body wall when it is displaced into spinning frictional engagement with thicker plastic end closure member. Therefore, prior to the invention, it was difficult to produce a continuous fluid tight seal in a composite container including a synthetic plastic end closure member spin bonded to the thin thermoplastic inner liner layer of a composite body member.
Furthermore, a conventional plastic end member which is bonded to a container body member has a tendency, when stressed during filling and handling of the container, to flex in such a manner that it peels away from the sides of the container where it is in bonding engagement therewith, thereby destroying the integrity of the seal between the end closure and body members.